1. Field of the Invention
The present invention relates to a cord-shaped heater and a sheet-shaped heater using the cord-shaped heater. The cord-shaped heater and the sheet shaped heater can be suitably used for an electric blanket, an electric carpet, a car seat heater and a steering heater, for example. In particular, the present invention related to the cord-shaped heater and the sheet-shaped heater having high flame retardancy and capable of preventing generation of spark if, by any chance, a disconnection fault occurs.
2. Description of Related Art
In general, a cord-shaped heater used for an electric blanket, an electric carpet, a car seat heater and the like is known to be formed by spirally winding a heating wire around a core wire and coating an outer cover made of an insulation body layer around them. Here, the heating wire is formed by paralleling or twisting a plurality of conductive wires such as copper wires and nickel-chromium alloy wires together. In addition, a heat-fused portion is formed on an outer periphery of the heating wire. The heating wire is adhered to a substrate such as a nonwoven fabric and an aluminum foil by the heat-fused portion (as shown in Patent document 1, for example).
In the conventional cord-shaped heater, the conductive wires are contact with each other. Therefore, when a part of the conductive wires is disconnected by being pulled or bended, the disconnected part is in the same state as when a diameter of the heating wire is reduced. As a result, a current amount per unit sectional area is increased at the disconnected part and overheating may be caused. On the other hand, it is also known that a heating wire formed by individually covering each of the conductive wires by an insulating film so that each of the conductive wires forms a part of a parallel circuit. By using the above configuration, even if a part of the conductive wires is disconnected, this only means that a part of the parallel circuit is disconnected. Thus, overheating can be prevented (as shown in Patent document 2 and Patent document 3, for example).
In addition, the applicant of the present invention filed Patent document 4 and Patent document 5 as a related technology.
[Patent document 1] Japanese Unexamined Patent Application Publication No. 2003-174952: KURABE INDUSTRIAL CO., LTD.
[Patent document 2] Japanese Unexamined Patent Application Publication No. S61-47087: Matsushita Electric Industrial Co., Ltd.
[Patent document 3] Japanese Unexamined Patent Application Publication No. 2008-311111: KURABE INDUSTRIAL CO., LTD.
[Patent document 4] Japanese Unexamined Patent Application Publication No. 2010-15691: KURABE INDUSTRIAL CO., LTD.
[Patent document 5] International Publication No. WO2011/001953: KURABE INDUSTRIAL CO., LTD.
When actually using the cord-shaped heater, various external forces such as tension and bending may be applied to the cord shaped heater. Since the conductive wires used for the cord-shaped heater are generally made of an extremely thin wire, the conductive wires may be disconnected when the external forces are applied. Even when the conductive wires are disconnected, there is no problem if both ends of the disconnected part are completely separated from each other. However, if the both ends are repeatedly contacted and separated with each other, a spark may be generated.
In Patent documents 2 and 3, various materials are described as the insulating film of the conductive wires. However, a so-called enameled wire is mainly used. In the enameled wire, organic materials such as a polyurethane resin and a polyimide resin are used as a material of the insulating film. When the spark is generated, the above described materials are melted or pyrolyzed by the heat and insulating function is lost. As a result, there is a problem that the exposed part of the conductive wires is increased and the spark can be generated more easily.
The present invention aims for solving the above described problem of the conventional technology. The present invention aims for providing a cord-shaped heater and a sheet-shaped heater using the cord-shaped heater having high flame retardancy and capable of preventing generation of spark if, by any chance, a disconnection fault occurs.